1. Field of the Invention
The present invention relates to a heat exchanger, more particularly to a total heat exchanger for exchanging sensible and latent heat between gas flows of different temperatures and humidities.
2. Description of the Prior Art
Heat exchangers are often used along with ventilation of air in a room or a vehicle. They exchange heat between the air discharged therefrom and introduced therein to recover the heat. Such heat exchangers must exchange both the sensible heat and latent heat of the air. This is referred to as "total heat exchange".
Well known conventional heat exchangers have a multi-layer structure formed by a plurality of spaced flat metal plates (partition plates) arranged in parallel to each other, for alternatively defining first and second gas flows, and a plurality of corrugated metal sheet members (spacer members) inserted between the partition plates, for maintaining the spaces between the partition plates. This type of metal heat exchanger can exchange only sensible heat, resulting in low efficiency heat exchange when there is a large amount of latent heat. That is to say, it cannot effectively conduct total heat exchange.
A known technique to solve this problem is to make the partition plates of material having a relatively low heat conductivity, such as asbestos, impregnated with a hydroscopic agent, such as lithium chloride, to recover the latent heat of the air. This type of partition plate, however, is low in permeability (defined here as the resistance of a material, such as a paper, to the permeation of a gas or liquid), and, therefore, polluted air flowing out of a room is returned again through the partition plate into the room.
It is also known to use Japanese paper, which is permeable to water vapor, for partition plates in a heat exchanger (see Japanese Examined Utility Model Publication (Kokoku) No. 50-22365). Japanese paper, however, is not that good in heat conductivity and water vapor permeability and it increases the size of a heat exchanger.